Treatment of hydrocarbon oil



Feb. 2, 1943. J. H. MccuLLouGH ETAL 2,309,651

TREATMENT 0F HYDRQCRBON OIL Filed Feb. 13, 1941 Paeaea ret. 2, 194sTREATMENT F HYDROCARBON OIL James H. McCullough and Edwin R. Birkhimer,

Philadelphia, and Leonard N. Leum, Upper. Darby, Pa., assignors to TheAtlantic Refining Company, Philadelphia, Pa., a corporation ofPennsylvania Application February 13, 1941, Serial No, 378,830

Claims.

The present invention relates to a method for removing acidic organiccompounds from hydrocarbon oil, and more particularly to the removal ofmercaptans and phenolic compounds from petroleum distillates.

An object of this invention is the provision of a simple and economicmethod embodying the desulfurizatlon of petroleum hydrocarbons bychemical agents and the regeneration of the chemical agents employed inthe desulfurizing treatment.

A further object of this invention is the desulfurization of petroleum'hydrocarbons, particularly naphthaand gasoline, by treatment thereofwith relatively small quantities of an aqueous solution of an alkalinereagent, and with an organic solvent.

A further object of this invention is a particular method of applyingthe treating agents to the hydyrocarbons to be desulfurized, and theregeneration of the agents employed in such treatment.

It has been proposed heretofore to desulfurize gasoline by treatmentwith dry sodium'hydroxide and anhydrous methyl alcohol, or withanhydrous alcoholic solutions of sodium hydroxide, or alcoholicsolutions of alkali agents containing various percentages of water.These prior art methods have been found impractical and uneconomic dueto the cost and difficulty of regenerating the spent treating agents,and to the necessity for recovering, at considerable cost, the alcoholretained in the treated gasoline.

However, these difliculties are overcome to substantial extent byoperating in accordance with the present invention, wherein relativelysmall quantities of treating agent are employed, regeneration of thespent agent issirnple and efficient, and a desulfurized oil is producedwhich is substantially free of treating agent.

Our invention comprises essentially countercurrently contacting anaqueous solution of an vent more soluble in the aqueous solution than inthe oil, forming a phase comprising oil having a reduced content ofacidic organic compounds and substantially free of solvent, and a secondphase comprising an aqueous alkaline solution containing the solvent andacidic organick compounds extracted from the oil, separating the phases,and subjecting the second mentioned phase to a regeneration treatment toseparate and recover the alkaline reagent, the solvent, and tliileacidic organic compounds removed from the o solvent, such as methanol,in a quantity of,'for

alkaline reagent with hydrocarbon oil and a sol- Our invention-may befurther understood with reference to the accompanying drawing, whichillustrates diagrammatically a system suitable for carrying out ourprocess.

Hyrocarbon oil, for example, gasoline, pref;- erably free of hydrogensulfide, and having acontent of 35 mg. sulfur as RSH per 100 cc., iscontinuously introduced through valve-controlled pipe i into the lowerpor/tion of extraction tower 2 provided with packing material 3 such asbroken pumice, tile, or the" like. An organic example, 0.5% by volume ofthe gasoline, is introduced into the lower portion of extraction tower 2through valve-controlled pipes 4 and 5, along with the gasoline flowingthrough valvecontrolled pipe l. Or, alternatively, the methanol may beintroduced at a higher elevation in tower 2 by means of pipe 6 and oneor more of va1ve-controlled pipes l, 8, and 9. An aqueous solution of analkaline reagent, for example,-

sodium hydroxide of 47% concentration, in a quantity of, for example, 2%by volume of the gasoline, is introduced into the upper portion of tower2 by means of valve-controlled pipe IU and pipe l I. The temperature inthe tower is maintained above the freezing point of the sodium hydroxidesolution, and temperatures of the orous alkaline solution, and theresulting aqueous alcoholic alkaline solution dissolves the mercaptidesand phenolates produced by the reaction of the sodium hydroxide with themercaptans and phenols originally contained in the gasoline. The rate offlow of the gasoline and the treating agent, and the point ofintroduction of themethanol is so adjusted that the treated gasolinewithdrawn from the top of tower 2 by means of valve-controlled pipe i2Vis substantially free of methanol and contains substantially less acidicorganic compounds than the gasoline charged to the tower. The treatedgasoline withdrawn from the tower by means of valve-controlled pipe I2may be passed through a iilter containing sand, pebbles, or clay toremove traces of entrained alkaline reagent, or such gasoline may besubjected to water washing, if desired. By employing the quantities ofalkaline solution and methanol above specified, the treated gasoline wasfound to contain 0.3 mg. sulfur as RSH per 100 cc.; and was sweet to thedoctor test. However, by varying the quantities and concentrations ofthe treating agents, either sweet or sour gasoline may be produced, suchgasoline containing a reduced or controlled amount of sulfur compounds.We have found that by introducing the methanol at an elevation in thetower, but below the point of introduction of the aqueous alkalinesolution, we are able to obtain better desulfurization than could beobtained if the methanol was introduced into the lower portion of thetower, along with the gasoline. In any event, the methanol must beintroduced at such an elevation in the tower that complete solution ofthe methanol in the aqueous alkaline solution is obtained before thegasoline reaches the top of the tower, otherwise a considerable quantityof methanol would pass from the tower in solution in the treatedgasoline.

Spent treating solution comprising an aqueous alcoholic solutioncontaining unreacted sodium hydroxide, sodium mercaptides andphenolates,y

methanol and traces of gasoline, is withdrawn from the bottom ofextraction tower 2 by means of valve-controlled pipe I3 and delivered bypump I4 through pipe I5 into the upper portion of stripping tower I6provided with packing I1, closed heating coil I8, and valve-controlledsteam jet I9. Heat is applied to the spent solution in tower I6 bycirculating steam through coil I8, or by injecting open steam into thesolution through valvecontrolled jet I9. Ihe temperature at the bottomof the tower may be of the order of 280 F., while that at the top of thetower is about 215 F.220 F. As a result of the heating, the mercaptidesare decomposed to mercaptans, with the liberation of an equivalentamount of sodium hydroxide, and the mercaptans, methanol, gasoline, anda portion of the watex` content of the spent solution are vaporized,withdrawn from the top of the tower through pipe 20, condensed incondenser 2|, and the condensate delivered by pipe 22 to separator 23.This condensate may comprise an aqueous solution containing 15%-30% byweight of methanol and 10-40 mg. sulfur as RSH per 100 cc., admixed withinsoluble mercaptans and traces of gasoline. The condensate is permittedto settle and stratify in separator 23, whereby there is formed an upperlayer of insoluble mercaptans and traces of gasoline, and a loweraqueous layer containing %-30% methanol and 10-40 mg. mercaptan sulfur.'I'he upper layer of insoluble mercaptans and traces of'gasoline isremoved from separator 23 by means of valve-controlled pipe 24, and maybe disposed of as desired. By this separation, 95% or more of themercaptans entering the separator with the condensate are removed fromthe aqueous methanol solution, only the lower molecular weightmercaptans remaining, to a small extent, in solution in the aqueousmethanol. To assist in the removal of the mercaptans soluble in theaqueous methanol, a. small amount of a solvent such as hydrocarbon oilor gasoline may be introduced into the separator by means ofvalve-controlled pipe 25. This oil, while immiscible with the aqueousmethanol, is capable of extracting therefrom a considerable portion ofthe mercaptans normally soluble in the aqueous methanol. The added oilcontaining the extracted mercaptans may be removed from the separator,together with the upper layer of normally insoluble higher molecularweight mercaptans.

The aqueous methanol solution containing traces of lower molecularweight mercaptans is withdrawn from the bottom of separator 23 andpassed by means of valve-controlled pipe 26 into fractionating tower 21provided with bubble trays 28, heating coil 29, and dephlegmating coil30. In the fractionating tower, the methanol and mercaptans arevaporizedand fractionally distilled from the aqueous methanol solution, thetemperature at the top of the tower being of the order of 150 F., and atthe bottom about 212 F. During the fractionation a small amount of wateris distilled over with the methanol and mercaptans, and the compositevapor is withdrawn from the top of tower 21 by means of valve-controlledpipe 3|, condensed .in condenser 32, and the condensate deliveredthrough pipe 33 to receiving tank 34. I'his condensate may comprisemethanol containing up to about 10% of Water and up to about 70 mg.mercaptan sulfur, substantially all of which is in the form of lowmolecular Weight mercaptans. The recovered methanol is withdrawn fromtank 34 and recycled by means of valve-controlled pipe 35, pipe 36, pump31, and pipe 6 to the extraction tower 2 for treatment of additionalquantities of gasoline.

As an alternative method of operating the fractionating tower 21, thefractionation may be carried out to produce a, liquid side stream ofmethanol which may be passed from tower 21 by means of valve-controlledpipe 38 into pipe 3B for recycling to extraction tower 2. constantboiling azeotrope of mercaptans and methanol is withdrawn from the topof fractionating tower 21 through valve-controlled pipe 39, condensed incondenser 40 and returned by pipe 4I to separator 23, wherein themercaptans and methanol may be separated to substantial extent. Thismethod of operating is particularly useful in the event that the aqueousmethanol supplied to tower 21 for fractionation contains excessiveamounts of low molecular weight mercaptans.

The water, comprising the bottoms or residue from the fractionaldistillation, is withdrawn from the bottom of tower 21 through pipe 42and may be recycled by means of pump 43, pipe 44, and either ofvalve-controlled pipes 45 and 46 to the stripping tower I6. This wateris substantially free of methanol but may contain small amounts ofmercaptan, i. e., of the order of 0.2 mg. mercaptan sulfur per 100 cc.If desired, a portion of the water may be diverted and introduced intoseparator 23 to assist in the separation of mercaptans from the stripperoverhead condensate, provided such condensate is decient in water. Inthe event that open steam is utilized in stripping tower I6, excessivewater may be removed from the system by means of valve-controlled pipe41 associated with fractionating tower 21. In the absence of open steamstripping, it will be obvious that a certain amount of fresh water willbe required to reach equilibrium operating conditions,

and this may be supplied by means of valve-cony trolled pipe 46.

In this event, aV

arator 50 by means of valve-controlled pipe 5I and disposed of asdesired, while the regenerated sodium hydroxide solution may be drawnfrom the bottom of the separator through pipe 52 and delivered by pump53 and pipes 5l and Il to the upper portion of extraction tower 2 foruse in the treatment of additional quantities of gasoline. However, wehave found that more complete desulfurization of the gasoline may beaccomplished by carrying out the treatment in extraction tower 2 in thepresence of recycled sodium phenolates. To accomplish this end, at leasta portion of the phenolates separated in separator 50 are withdrawntherefrom by means of valvecontrolled pipe 55 and passed, together withrecycle methanol, through pipe 36 to pump 31, and

delivered thereby through pipe 6 to the extraction tower 2.

While in the operation of our system as above' described, we have shownthe use of a single extraction tower 2 in whch removal of acidic organiccompounds from gasoline may be accomplished, we may employ in lieuthereof, two extraction towers in series since two short towers are moreconvenient to build and operate than a single tall tower. In such case,the aqueous solution of sodium hydroxide is introduced into the upperportion of the rst tower, flowed downwardly through the first tower anddrawn from the bottom thereof, mixed with methanol, and the aqueousmethanol solution of sodium hydroxide then introduced into the upperportion of the second tower. This solution is then flowed downwardlythrough the second tower vandis withdrawn from the bottom thereof.Simultaneously, the gasoline to be treated is introduced into the lowerportion of the second tower, flowed upwardly in intimate countercurrentcontact with the descending aqueous methanol solution of sodiumhydroxide whereby acidic organic compounds are extracted, and thetreated gasoline containing some dissolved methanol is drawn from thetop of the second tower. This treated gasoline is then introduced intothe lower portion of theflrst tower, flowed upwardly therethrough inintimate countercurrent contact with the descending aqueous solution ofsodium hydroxide and is then withdrawn from the top of the first tower.The gasoline so Withdrawn is substantially free of methanol and has asubstantially reduced content of acidic organic compounds. The spenttreating solution from the bottom of the second tower may be regeneratedin accordance' with the method hereinbefore described, and the recoveredsodium hydroxide solution and methanol recycled for the treatment ofadditional quantities of gasoline. Thus, the two towers in seriesfunction in the same manner as the single extraction tower 2, the rsttower corresponding to the upper portion of tower 2 and the second towercorresponding to the lower portion of tower 2. A continuouscountercurrent ow is maintained through the two towers, in exactly thesame manner as in tower 2.

In the description of our process given hereinbefore, we have indicatedthat gasoline may be substantially desulfurized by treatment with 2% byvolume of 47% sodium hydroxide and 0.5% by volume of methanol.v It is tobe understood, however, that we may treat hydrocarbons other thangasoline, for example, gaseous hydrocarbons, liquefied normally gaseoushydrocarbons, naphtha, kerosine, furnace oil, gas oil, and other higherboiling hydrocarbons. Furthermore, the quantity and concentration of theaqueous solution of alkaline reagent may be varied considerably. Forexample, the quantity of aqueous alkaline solution employed may rangefrom 1% or 2% by volume to as much as 100% by volume,

based on the hydrocarbons to be treated, while the concentration ofalkaline reagent in the aqueous solution may be of the order of 10% to50% by weight. We prefer to use relatively strong aqueous solutionscontaining from about 35% to about 47% by weight of alkaline reagent.While sodium hydroxide is preferred because of its availability andcheapness, other alkaline reagents may be used, including sodiumcarbonate, sodium phenolates, sodium alcoholates, potassium hydroxide,carbonate, or phenolate, potassium alcoholates, potassium isobutyrate,ammonia, ammonium hydroxide, strong organic bases such as amines,hydroxyamines, guanldine, quaternary ammonium bases, and the like, ormixtures of two or more of these alkaline reagents.

We prefer to employ as our organic solvent. methanol, although otherlower aliphatic alcohols may be employed in lieu of or admixed withmethanol. Solvents which are more soluble in an aqueous solution ofalkaline reagent than in hydrocarbons are particularly useful in ourprocess, including ethanol, propanol, isopropanol, ethylene glycol andthe homologous glycols, the glycol ethers, ethylene chlorhydrin,glycerol, acetone,

ethylmethyl ketone, and the like. 'I'hese solvents may be employed in ananhydrous condition, or in admixture with water. For example, anhydrousmethanol, or methanol containing up to of water may be utilized.Methanol solutions containing from about 10% to about 80% of water, whenused in coniunction with concentrated solutions of an alkaline reagent,such as sodium hydroxide, have been found particularly elective.

What we claim is:

1. The method of removing acidic organic com.v pounds from hydrocarbonoil containing the same, which comprises introducing an aliphaticalcohol containing less than 4 carbon atoms per molecule into a streamof said hydrocarbon oil, and countercurrently contacting Vthe said oilstream with a stream of an aqueous solution of an alkalinereagent inwhich said alcohol is more soluble than in the hydrocarbon oil, wherebythe alkaline reagent will admix with the alcohol in the oil stream andthe mixture will act upon the oil stream to remove acidic organiccompounds therefrom, the point of introduction of said alcohol being inadvance of the point of introduction of said alkaline reagent andsufciently removed therefrom to elect extraction of entrained alcoholfrom the oil stream.

2. 'I'he method of removing mercaptans from hydrocarbon oil containingsame. which comprises introducing methanol into a stream of vsaidhydrocarbon oil, and countercurrently contacting said oil stream with astream of an aqueous solution of sodium hydroxide in which the methanolis more soluble than in the hydrocarbon oil, whereby the sodiumhydroxide solution will admix with the methanol in the oil stream andthe mixture will act upon the oil stream to remove mercaptans therefrom,the point of introduction of the methanol being in advance of the pointof Y introduction of the sodium hydroxide solution and sufiicientlyremoved therefromto effect extraction of entrained methanol from the oilstream.

3. The method of removing acidic organic compounds from hydrocarbon oilcontaining the same, which comprises countercurrently contacting astream of said hydrocarbon oil with a stream of an aqueous solution ofan alkaline reagent, and introducing into said streams an aliphaticalcohol containing 4less than 4 carbon atoms per molecule, whereby thealkaline reagent and alcohol will admix and the admixture will act uponthe oil stream to remove acidic organic compounds therefrom, the pointof introduction of the alcohol being in advance of the point ofintroduction oi.' the alkaline reagent and suillciently removedtherefrom to effect extraction of entrained alcohol from the oil stream.

4. The method of removing mercaptans from hydrocarbon oil containing thesame, which comprises countercurrently contacting a stream of` saidhydrocarbon oil with a stream of an aqueous solution of sodiumhydroxide, and introducing methanol into said streams, whereby thesodium hydroxide solution and the methanol will admix and the admixturewill act upon the oil stream to remove mercaptans therefrom, the pointof introduction of the methanol being in advance of the point ofintroduction of the sodium hydroxide solution and sufficiently removedtherefrom to effect extraction of entrained methanol from the oilstream.

5. The method of removing acidic organic compounds from hydrocarbon oilcontaining the same, which comprises introducing an aqueous solution ofan alkaline reagent into the upper portion oi' an extraction zone.introducing said hydrocarbon oil into the lower portion of said zone,introducing an aliphatic alchol containing less than 4 carbon atoms permolecule into said zone at a point in advance o! the point ofintroduction of the alkaline reagentand suiciently removed therefrom toeffect extraction of entrained alcohol from the oil, countercurrentlycontacting the alkaline reagent with the oil and alcohol, whereby thealkaline reagent and alcohol will act upon the oil to extract acidicorganic compounds therefrom, withdrawing from the upper portion of saidzone oil having a reduced content of acidic organic compounds andsubstantially i'ree of alcohol, and withdrawing from the lower portionof said zone an aqueous alkaline solution containing the alcohol andacidic compounds extracted from the oil.

JAMES H. MCCULLOUGH. EDWJIJ R. BIRKHIMER. LEONARD N. LEUM.

